A piezoelectric/electrostrictive actuator has an advantage that displacement can be controlled in a submicron order with accuracy. In particular, a piezoelectric/electrostrictive actuator, in which a sintered body of a piezoelectric/electrostrictive ceramic composition is used, has advantages such as high electromechanical conversion efficiency, large generating force, high response speed, high durability and less power consumption, in addition to the advantage that displacement can be controlled with accuracy. Thanks to these advantages, the piezoelectric/electrostrictive actuator is used in a head of an inkjet printer, an injector of a diesel engine, a hydraulic servo valve, a head of VTR, a pixel of a piezoelectric ceramic display and the like.
An example of the conventional piezoelectric/electrostrictive actuator as described above will be described with reference to FIG. 30. FIG. 30 is a schematic view of a conventional piezoelectric/electrostrictive element 8 used as an actuator in a head of an inkjet printer, which is a cross-sectional view of the piezoelectric/electrostrictive element 8.
As shown in FIG. 30, the piezoelectric/electrostrictive element 8 has a structure in which a lower layer electrode film 812, a lower layer piezoelectric/electrostrictive film 816, an inner layer electrode film 818, an upper layer piezoelectric/electrostrictive layer 820 and an upper layer electrode film 814 are laminated in this order on a thin portion 804 of a substrate 802. In the piezoelectric/electrostrictive element 8, a driving signal is applied between an outer layer electrode film (lower layer electrode film 812 and upper layer electrode film 814) 810 and the inner layer electrode film 818, whereby the thin portion 804 and a laminate 808, which is composed the lower layer electrode film 812, the lower layer piezoelectric/electrostrictive film 816, the inner layer electrode film 818, the upper layer piezoelectric/electrostrictive film 820 and the upper layer electrode film 814, can be subjected to bending vibration.
Japanese Patent Application Laid-Open No. 2006-202990 is a prior art reference related to a conventional piezoelectric/electrostrictive element. Japanese Patent Application Laid-Open No. 2006-202990 discloses a piezoelectric/electrostrictive element in which a film thickness of a piezoelectric/electrostrictive film is uniform (see FIG. 9) and a piezoelectric/electrostrictive element in which a film thickness of a piezoelectric/electrostrictive film continuously becomes thinner from a center portion thereof toward an edge portion thereof (see FIG. 10).
However, in the conventional piezoelectric/electrostrictive element, a displacement amount becomes insufficient in some cases. In addition, there arises a problem that, when the film thickness of the piezoelectric/electrostrictive film is made thinner overall for increasing the displacement amount, dielectric breakdown is likely to occur at high humidity at an edge portion of an operating region in which electrode films are opposed to each other with the piezoelectric/electrostrictive film being sandwiched therebetween.